1. Field of the Invention
This invention relates to the manufacture of cellular polyurethane plastics, i.e., polyurethane foams, and in particular, the invention relates to the making of a suitable curing agent or cross-linking agent for use in the making of such compositions.
2. Description of the Prior Art
It is known, for example, from U.S. Pat. No. 2,850,464, that in the making of polyurethane foams, it is often desirable to include in the composition a certain amount of a polyfunctional curing agent. In the early days of this art, the curing agent was usually a trifunctional or high alcohol, such as glycerol, pentaerythritol, sorbitol, or the like. As early as 1953, it was also appreciated that diamines could be used for this purpose. The above-mentioned patent mentions the possibility of using methylene dianiline (MDA) as the curing agent, but later experience with this compound has revealed that for most purposes, it is too reactive to be useful as a curing agent. When it is included in a polyurethane foam formulation, the curing time tends to be so short that it becomes impractical to make effective use of the composition, because the material hardens before the foam-forming reaction has taken place to a sufficient extent.
Previous efforts have been made to provide compounds similar to MDA but somewhat lower in reactivity. An example is U.S. Pat. No. 3,563,906, which teaches that MDA is unsatisfactory, and that it has been common to use in place of it other hindered or suitably substituted aromatic diamines, such as 2,2'-dichlorobenzidene or 4,4'-methylene-bis-(2-chloroaniline) (MOCA). The above-mentioned patent then goes on to teach the making of a composition containing MOCA and various other diamines, starting with a crude material resulting from the reduction of chloronitrobenzene.
Still more recently, it has developed that MOCA and compositions that contain it are considered of limited usefulness, because of the suspected cancer-producing properties of MOCA. Efforts have been made to find a satisfactory substitute for MOCA.
Both MDA, on the one hand, and the lower polyalkylene oxides, ethylene oxide and 1,2-propylene oxide, are well known as chemicals, and it has been known that MDA and other diamines will react with any of such polyalkylene oxides.
Polyurethane compositions have been made which contain, as a part thereof, a polymeric material made by reacting MDA with several mols of polyalkylene oxide. Polyurethane compositions frequently contain a polyol or polyester-polyol component that is used to react with a polyisocyanate material to make up the polymeric material that comprises the bulk of the composition. Such polyols are not, of course, useful as curing agents or cross-linking agents in the manufacture of cellular polyurethane compositions, as MOCA and compositions similar to it, or containing it, have customarily been.
The idea of reacting an aliphatic diamine, namely, ethylenediamine, with fewer than 4 moles of alkylene oxide, to obtain useful products, has been disclosed in U.S. Pats. Nos. 3,398,097; 3,398,198; 3,454,647; and 3,524,883.